The requirements for monitoring and controlling stack gas pollutants have resulted in the development of solid electrolyte gas sensors having electrolyte compositions uniquely responsive to gaseous pollutants such as SO.sub.x, CO.sub.x and NO.sub.x. Solid electrolyte sensors for monitoring gases containing anhydrides or related compounds in air or in oxygen-bearing gases have been described in detail in Canadian Pat. Nos. 1,002,599 and 1,040,264, both of which have been assigned to the assignee of the present invention and are incorporated herein by reference. In typical industrial installations a separate solid electrolyte gas sensor is employed to measure oxygen in the stack gas environment. The above-referenced sensors are electrochemical concentration cells which sense the equilibrium of a gas species of interest and generate a Nernst equation EMF signal corresponding to the difference in partial pressure of the gas species across the solid electrolyte sensor. Typically, the solid state sensor includes an ion conductive solid electrolyte with electrodes disposed on opposite surfaces thereof. The stack gas, or monitored gas environment, contacts a sensing electrode while the opposite electrode serves as a reference electrode. Conventional solid electrolyte compositions require operating temperatures of between about 600.degree. C. and 900.degree. C. to exhibit the desired ion conductivity to generate a suitable EMF signal. The accuracy of the EMF measurement depends in part on the effective sealing, or isolation, of the reference electrode from the monitored gas environment contacting the sensing electrode of the electrochemical cell. This isolation, or sealing requirement, at elevated operating temperatures has resulted in numerous expensive and complicated designs to achieve the desired isolation.